Classification of Measuring Instruments

Classification of Measuring Instruments

Measuring instruments may be broadly classified as follows

1.       Absolute instruments

2.       Secondary instruments

(a)     Indicating instruments

(b)     Integrating instruments 

(c)     Recording  instruments

Absolute and secondary instruments

 Absolute instruments: “absolute instruments are those which gives the value of the quantity to be measured, in terms of the constants of the instruments and their deflection only”.

Such instruments do not require any previous calibration or comparison.

Example: Tangent galvanometer (is a very common example) and Rayleigh’s current balance instruments.

Uses: These instruments used as standardizing instruments in laboratories.

Secondary instruments: “secondary instruments are those in which the value of electrical quantity to be measured can be determined from the deflection of the instruments”.

Such instruments are need to be pre-calibrated by comparison with an absolute instrument. Without calibration, the deflection of such instruments is meaningless.

Example: An ammeter, voltmeter, a glass thermometer, and a pressure gauge instruments.

Uses: These instruments are generally used in practical work.